This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-352888 filed on Dec. 4, 2002.
1. Field of the Invention
The present invention relates to a commutator, a motor having the commutator and a manufacturing method of the commutator.
2. Description of Related Art
Some previously proposed electric motors have a commutator that includes a plurality of commutator segments that are slidably engaged with power supply brushes and are divided into a plurality of groups, each of which includes two or more of the commutator segments electrically connected together to shortcircuit therebetween. In such a motor, electric current is supplied not only to the directly contacting commutator segments, which directly contact the power supply brushes, but also to the indirectly contacting commutator segments, which indirectly contact the power supply brushes through one of the directly contacting commutator segments. Such an arrangement allows a reduction in the number of the power supply brushes.
In some cases, the electrical connection of the commutator segments included in each group is achieved by short-circuiting wires, which interconnect the commutator segments of each group. In other cases, the electrical connection of the commutator segments included in each group is achieved by bypassing armature winding coils, which are wound around a core of the motor, to the corresponding commutator segments.
Furthermore, Japanese Unexamined Patent Publication No. 2001-320862, which corresponds to U.S. Patent Application Publication No. US 2001/0038252 A1, discloses another technique for electrically interconnecting the commutator segments of each group of the commutator. Here, an equalizer assembly, i.e., a sort-circuiting assembly, which includes a plurality of terminals for electrically connecting the commutator segments of the respective groups, is arranged next to the commutator segments in the axial direction. However, this arrangement disadvantageously causes an increase in a size of the motor since the equalizer assembly requires additional axial space in the motor.
Also, Japanese Unexamined Patent Publication No. 11-187622 discloses another technique for electrically interconnecting the commutator segments of each group. Here, a plurality of short-circuiting parts is provided in a commutator. Each short-circuiting part interconnects between corresponding two commutator segments and is formed integrally with the two commutator segments. More specifically, at one axial end of the commutator, one end of one of the two commutator segments is connected to one end of the other one of the two commutator segments by the short-circuiting-part. The short-circuiting part is bent in the axial direction of the commutator and is then bent in a circumferential direction of the commutator and is bent in the axial direction of the commutator once again to connect the ends of the two commutator segments, which are located in the same axial end of the commutator. An axial extent of one of the short-circuiting parts differs from another one of the short-circuiting parts to avoid short-circuiting between these short-circuiting parts. However, this arrangement requires advance preparation of different pairs of commutator segments, each of which has a short-circuiting part of a different axial extent. This causes an increase in types of components of the commutator and causes an increase in a manufacturing cost or causes an increase in manufacturing time.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a commutator having a minimized number of components and a minimized axial size. It is another objective of the present invention to provide a motor having such a commutator. It is another objective of the present invention to provide a method for manufacturing such a commutator.
To achieve the objectives of the present invention, there is provided a commutator for an electric motor that includes a plurality of power supply brushes, which are slidably engaged with the commutator. The commutator includes a plurality of conductive commutator segments, a plurality of generally planar short-circuiting parts and a dielectric body. The conductive commutator segments are arranged at generally equal angular intervals in a circumferential direction of the commutator. The commutator segments are divided into a plurality of groups, each of which includes two or more of the commutator segments. The generally planar short-circuiting parts are respectively provided to the groups of the commutator segments and are located radially inward of the commutator segments in such a manner that the short-circuiting parts are spaced one after the other in an axial direction of the commutator. Each short-circuiting part is seamlessly and integrally formed with and is electrically connected to at least a portion of each commutator segment of a corresponding one of the groups of the commutator segments. At least one of the short-circuiting parts is located within an axial extent of at least one of the power supply brushes measured in the axial direction of the commutator. The dielectric body securely holds each commutator segment and each short-circuiting part.
To achieve the objectives of the present invention, there is provided an electric motor that includes a stator, a rotor and a plurality of power supply brushes. The stator includes a plurality of field poles. The rotor is rotatable relative to the field poles and includes the above-described commutator. The power supply brushes are slidably engaged with the commutator.
To achieve the objectives of the present invention, there is provided a method for manufacturing a commutator that includes a plurality of commutator segments arranged at generally equal angular intervals. In the method, a plurality of conductive blank plate members is stacked in such a manner that the blank plate members are circumferentially displaced from one another by a predetermined angle. Each blank plate member includes an annular part and a short circuiting part, and the short circuiting part is located radially inward of the annular part and is connected to a plurality of points of the annular part, which are arranged at generally equal angular intervals in the circumferential direction of the annular part. Then, a dielectric material in a liquid phase is filled in a space defined radially inward of the annular parts of the blank plate members. Thereafter, the dielectric material is solidified. Next, the annular part of each blank plate member is radially cut at a plurality of predetermined cut points, which are circumferentially arranged at generally equal angular intervals, to divide the annular part of the blank plate member into a plurality of portions, each of which serves as a sub-element of a corresponding one of the commutator segments.